Resin caulking cartridges, because of their superior ability to contain and preserve certain caulking materials, are supplanting paper caulkers. Resin caulker cartridges are also being used for a wider range of caulking compounds, and this has led to a problem that is solved by the invention.
Some caulking materials have a relatively large coefficient of thermal expansion and can also give off gas during storage. This requires expansion room, and because of the limitations from other parameters, these materials tend to force the caulker plunger rearwardly out of the rear end of the caulker during storage at high temperatures. This liberates the caulker contents and creates a messy loss.
A partial solution to this problem is making the caulker barrels relatively thin-walled so that the barrel can bulge some as the contents expand. The pressure available to bulge the barrel wall is limited to the pressure the plunger can contain, however, so that this solution offers less than adequate security against plunger backout.
The inventive solution is a plunger backout stop formed in the right shape at the rear end of the cartridge barrel by a particular method and apparatus that makes the stop practical, reliable, and economical for mass-produced caulkers. The shape of the stop allows easy insertion of the plunger into the barrel and reliably prevents plunger backout. The apparatus is economical, the process is speedy, and the desired shape is acheived at very low cost.